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1. General Principles & Basic Science MCQs

Practice Set 34 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 661

Topic: 1. General Principles & Basic Science

Which type of joint lubrication mechanism is most critical during low-load, low-speed activities such as standing or beginning to walk?

. Hydrodynamic lubrication
. Elastohydrodynamic lubrication
. Weeping lubrication
. Boundary lubrication
. Squeeze-film lubrication

Correct Answer & Explanation

. Boundary lubrication

Explanation

Boundary lubrication, mediated by lubricin (PRG4) binding to the articular surface, prevents wear during high-load/low-speed or low-load/low-speed starting conditions. Fluid-film mechanisms dominate at higher speeds.

Question 662

Topic: Biology, Genetics & Bone Healing

Which enzyme is responsible for the conversion of 25-hydroxyvitamin D to its most active form, 1,25-dihydroxyvitamin D, and where is it predominantly located?

. 25-hydroxylase in the liver
. 1-alpha-hydroxylase in the kidney
. 24-hydroxylase in the bone
. 7-dehydrocholesterol reductase in the skin
. Alkaline phosphatase in osteoblasts

Correct Answer & Explanation

. 1-alpha-hydroxylase in the kidney

Explanation

The enzyme 1-alpha-hydroxylase, located in the proximal convoluted tubules of the kidney, converts 25-hydroxyvitamin D into the active hormone 1,25-dihydroxyvitamin D. This conversion is heavily stimulated by parathyroid hormone (PTH).

Question 663

Topic: Infection, Pharmacology & VTE

According to the Kocher criteria, which combination strongly differentiates septic arthritis of the hip from transient synovitis in a pediatric patient?

. ESR > 40 mm/hr, WBC > 12,000, inability to bear weight, fever > 38.5 C
. CRP > 2.0 mg/dL, WBC > 10,000, morning stiffness, rash
. Radiographic joint space widening, ESR > 20, positive Barlow test
. History of recent URI, low-grade fever, limp
. Ultrasound showing effusion, afebrile, normal inflammatory markers

Correct Answer & Explanation

. ESR > 40 mm/hr, WBC > 12,000, inability to bear weight, fever > 38.5 C

Explanation

The Kocher criteria include non-weight-bearing status, ESR > 40 mm/hr, fever > 38.5 C, and a WBC count > 12,000 cells/mm3. The presence of all four criteria yields a 99% predictive probability for septic arthritis.

Question 664

Topic: Biology, Genetics & Bone Healing

A patient with osteopetrosis is found to have defective osteoclast function. The failure of osteoclasts to create an acidic environment for bone resorption is most commonly due to a mutation affecting which of the following?

. Cathepsin K
. Carbonic anhydrase II
. RANK ligand
. Osteoprotegerin
. Tartrate-resistant acid phosphatase (TRAP)

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Osteopetrosis is often caused by a deficiency in Carbonic Anhydrase II, essential for generating protons. These protons are pumped into the ruffled border to create the acidic environment required to dissolve mineralized bone.

Question 665

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) initiate the osteoinductive cascade by binding to transmembrane receptors. This binding directly phosphorylates and activates which intracellular signaling molecules?

. JAK/STAT
. Wnt/beta-catenin
. Smad 1, 5, and 8
. c-AMP
. NF-kappa B

Correct Answer & Explanation

. Smad 1, 5, and 8

Explanation

BMPs bind to serine/threonine kinase receptors on the cell surface, phosphorylating intracellular Smad proteins (1, 5, and 8). These form a complex with Smad 4 and translocate to the nucleus to regulate gene transcription for osteoblast differentiation.

Question 666

Topic: Infection, Pharmacology & VTE
A patient is prescribed fondaparinux for DVT prophylaxis following total hip arthroplasty. What is the specific mechanism of action of this medication?
. Direct thrombin inhibitor
. Vitamin K antagonist
. Indirect selective inhibitor of Factor Xa via antithrombin III
. Direct selective inhibitor of Factor Xa
. Inhibitor of ADP-induced platelet aggregation

Correct Answer & Explanation

. Indirect selective inhibitor of Factor Xa via antithrombin III

Explanation

Fondaparinux is a synthetic pentasaccharide that binds to antithrombin III, causing a conformational change that indirectly and selectively inhibits Factor Xa. Unlike Rivaroxaban, it is not a direct Factor Xa inhibitor.

Question 667

Topic: 1. General Principles & Basic Science

According to the Seddon classification, which type of peripheral nerve injury involves complete disruption of axons and myelin sheaths, but preservation of the endoneurium, perineurium, and epineurium?

. Neurapraxia
. Axonotmesis
. Neurotmesis
. Wallerian degeneration
. Neuroma-in-continuity

Correct Answer & Explanation

. Axonotmesis

Explanation

Axonotmesis involves the interruption of axons and their myelin sheaths with preservation of the surrounding connective tissue framework (endoneurium). This architectural preservation allows for spontaneous recovery as regenerating axons are guided to their original targets.

Question 668

Topic: Biology, Genetics & Bone Healing
During the soft callus phase of secondary fracture healing, which type of collagen is primarily synthesized by the proliferating chondrocytes?
. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type II

Explanation

During the soft callus phase, chondrocytes proliferate and primarily synthesize Type II collagen (cartilage matrix). As the callus matures into hard bone, osteoblasts replace this with Type I collagen.

Question 669

Topic: Biomechanics & Biomaterials

Which element is specifically added to stainless steel alloys (e.g., 316L) to improve their resistance to pitting corrosion in the chloride-rich environment of the human body?

. Carbon
. Nickel
. Molybdenum
. Chromium
. Manganese

Correct Answer & Explanation

. Molybdenum

Explanation

Molybdenum is added to 316L stainless steel specifically to enhance resistance to pitting and crevice corrosion. Chromium provides the general passivation layer, while carbon is kept low (the "L" in 316L) to prevent intergranular corrosion.

Question 670

Topic: Biomechanics & Biomaterials

Which of the following antibiotics is most frequently added to polymethylmethacrylate (PMMA) bone cement due to its broad-spectrum efficacy and thermal stability during the exothermic polymerization process?

. Penicillin G
. Ceftriaxone
. Tobramycin
. Tetracycline
. Ciprofloxacin

Correct Answer & Explanation

. Tobramycin

Explanation

Tobramycin, gentamicin, and vancomycin are the most common antibiotics mixed into PMMA. They are chosen because they are available in powder form, have broad-spectrum coverage, and are thermostable during the high-heat curing of cement.

Question 671

Topic: 1. General Principles & Basic Science

Which of the following properties is the same for both botulinum toxin types A and B:

. Dose
. Duration of action
. Antigenicity
. Mechanism of action
. Molecular structure

Correct Answer & Explanation

. Antigenicity

Explanation

There are seven serologic subtypes of botulinum toxin, and only two are approved for clinical use. The duration of action of type A is slightly longer and it is less antigenic. Both type A and B have different structures. The dose of type A is lower in absolute units. Both have the same site of action they inhibit the release of acetylcholine from the neuromuscular junction, although they act on different proteins inside the cell.

Question 672

Topic: 1. General Principles & Basic Science

Stickler syndrome is caused by a mutation in the gene for which of the following:

. Collagen
. Fibrillin
. Glycoprotein
. Osteopontin
. Fibroblast growth factor

Correct Answer & Explanation

. Collagen

Explanation

Stickler syndrome is characterized by premature osteoarthritis in multiple joints, visual complications, auditory defects, and cleft palate. Stickler syndrome is caused by a defect in the genes for type 2 or type 11 collagen.

Question 673

Topic: 1. General Principles & Basic Science

Stickler syndrome is characterized by all of the following features except:

. Visual disorders
. Hearing problems
. Degenerative joint disease
. Significant short stature
. Irregular vertebral endplates

Correct Answer & Explanation

. Significant short stature

Explanation

Stickler syndrome, also known as hereditary arthro-ophthalmopathy, is characterized by visual problems, progressive hearing loss, and malar or mandibular hypoplasia. In terms of orthopedic complications, most patients develop premature degenerative joint disease and disk abnormalities, including narrow and irregular endplates. Significant short stature is not common in patients with Stickler syndrome.

Question 674

Topic: Infection, Pharmacology & VTE

Which of the following is the most common site for primary epiphyseal osteomyelitis:

. Proximal femur
. Distal femur
. Proximal tibia
. Distal tibia
. Proximal humerus

Correct Answer & Explanation

. Distal femur

Explanation

Osteomyelitis of the epiphysis is less common than osteomyelitis of the metaphysis. Osteomyelitis of the epiphysis may occur from spread across transphyseal vessels or primary hematogenous seeding. The most common location is the distal femoral epiphysis, and it most commonly affects infants and young children.

Question 675

Topic: Infection, Pharmacology & VTE

A normal (negative) result is used to rule out septic arthritis of the hip on which of the following tests:

. Plain radiographs
. Ultrasound
. C ulture of joint fluid
. C-reactive protein
. None of the above

Correct Answer & Explanation

. None of the above

Explanation

False-negative results may occur with each of the tests. C ulture results may be negative in up to a quarter of patients. Ultrasound may be false-negative in up to 20% of patients with septic arthritis of the hip. C-reactive protein may be normal early in the course of disease. The diagnosis is based upon a constellation of findings, including clinical examination.Correct Answer: None of the above

Question 676

Topic: 1. General Principles & Basic Science

Which of the following is a contraindication to the use of vacuum assisted closure (VAC ):

. A deep surgical wound
. An acute soft tissue wound
. A wound with necrotic muscle that has not been debrided
. A fresh, split-thickness skin graft
. A chronic wound that is slow to close

Correct Answer & Explanation

. A wound with necrotic muscle that has not been debrided

Explanation

Vacuum assisted closure (VAC ) should be applied to infected or damaged tissue after debridement. All of the other possible answer choices are conditions for which VAC is appropriate.

Question 677

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with an expansile, purely lytic lesion in the distal femur epiphysis extending to the subchondral bone. Which of the following systemic medications serves as a targeted adjunct to surgical treatment for this specific pathology?

. Imatinib
. Denosumab
. Rituximab
. Bevacizumab
. Doxorubicin

Correct Answer & Explanation

. Denosumab

Explanation

Giant cell tumors of bone consist of neoplastic stromal cells that express RANKL, which recruits normal osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, is an effective adjunctive treatment to halt bone destruction.

Question 678

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with a recurrent giant cell tumor of the distal radius. She is started on denosumab therapy. What is the precise mechanism of action of this medication?

. Inhibits osteoprotegerin (OPG)
. Binds and neutralizes RANKL
. Directly induces apoptosis in the multinucleated giant cells
. Inhibits vascular endothelial growth factor (VEGF)
. Blocks the mutated GNAS1 receptor

Correct Answer & Explanation

. Binds and neutralizes RANKL

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from activating RANK on the surface of osteoclasts and giant cells. This arrests the osteolytic activity characteristic of giant cell tumors of bone.

Question 679

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with an eccentric, lytic epiphyseal-metaphyseal lesion of the distal femur. Biopsy confirms a giant cell tumor of bone. If medical therapy is considered, which of the following molecular targets is specifically inhibited to reduce osteoclast-mediated bone resorption?

. Vascular Endothelial Growth Factor (VEGF)
. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Mammalian Target of Rapamycin (mTOR)
. Tyrosine kinase
. Programmed cell death protein 1 (PD-1)

Correct Answer & Explanation

. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)

Explanation

The neoplastic stromal cells in a giant cell tumor of bone express high levels of RANKL, which recruits and activates the reactive multinucleated giant cells. Denosumab, a monoclonal antibody against RANKL, is utilized as targeted medical therapy for advanced or unresectable cases.

Question 680

Topic: Biology, Genetics & Bone Healing

Denosumab is frequently used in the management of unresectable or recurrent giant cell tumors of bone. Which of the following is the specific molecular target of this medication?

. Osteoprotegerin (OPG)
. Vascular endothelial growth factor (VEGF)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Tumor necrosis factor-alpha (TNF-alpha)
. Macrophage colony-stimulating factor (M-CSF)

Correct Answer & Explanation

. Receptor activator of nuclear factor kappa-B ligand (RANKL)

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, inhibiting its interaction with RANK on osteoclasts and osteoclast precursors. In giant cell tumors, the neoplastic stromal cells overexpress RANKL, which recruits the destructive reactive multinucleated giant cells.

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